*PhD student position at Stockholm University* We are recruiting a fully funded 4-year PhD student position for a project examining how sexual selection acts in females and using a small freshwater fish, the pygmy halfbeak (Dermogenys collettei), as a model. Female halfbeaks express a conspicuous sexual ornament???an orange abdominal gravid spot that males use when making mate choice decisions. This trait allows experimental manipulation of female ornamentation, providing an exceptional opportunity to test key evolutionary hypotheses. The PhD project will combine laboratory experiments, fieldwork in Southeast Asia (Malaysia and Singapore), and AI-assisted behavioural tracking to examine the costs, benefits, and ecological drivers of female sexual ornaments in halfbeaks. The project integrates evolutionary biology, behavioural ecology, and sensory ecology, and uses state-of-the-art automated tracking and phenotypic manipulation techniques. Therefore, we are looking for a person with a strong interest and training in evolutionary biology and behavioural research. The PhD student will join the research group of Prof. John Fitzpatrick (www.su.se/english/profiles/j/jfrit) at the Department of Zoology, Stockholm University, located in the city of Stockholm, Sweden. The Department of Zoology has an international working atmosphere, with researchers and students from across the world. The working language is English and the position offers plenty of opportunities for scientific exchange with evolutionary biologists and behavioural ecologists. Overseas applications are encouraged. The complete ad with information on qualification requirements and instructions on how to apply is at: https://su.varbi.com/en/what:job/jobID:893229/ Application deadline: February 15, 2026 For inquiries about the position, please contact John Fitzpatrick: john.fitzpatrick@zoologi.su.se John Fitzpatrick Professor Department of Zoology Stockholm University 106 91 Stockholm Sweden Lab website: https://sites.google.com/view/fitzpatrick-lab/home John Fitzpatrick (to subscribe/unsubscribe the EvolDir send mail to golding@mcmaster.ca)